1. Field of the Invention
The present invention relates to a scroll type compressor provided with a fixed scroll, an orbiting scroll revolvable around the fixed scroll, and compression chambers defined between the fixed scroll and orbiting scroll, such that the volumes of the compression chambers are reduced in accordance with the revolution of the orbiting scroll.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 59-58187 (corresponding to U.S. Pat. No. 4,547,137) discloses a scroll type compressor in which the central tip portions of spiral elements of a fixed scroll and an orbiting scroll are formed thicker in order to improve the durability of the central tip portions and reduce the size and weight of the overall compressor.
This conventional compressor will be described in more detail. The inner wall and outer wall of each of the spiral elements of the scrolls are formed along involute curves. The starting points of the involute curves of the inner and outer walls are separated by 180.degree.. Further, the central tip portions have flat inner walls facing each other, which are formed along a line which linearly connects both starting points. The central tip portion of each scroll is approximately semicircular, and is relatively thicker than in previous scroll type compressors. This design improves the mechanical strength of the central tip portion of each spiral element.
In the conventional scroll type compressor, the flat inner walls of the central tip portions of both scrolls come into close contact with each other. The discharge port provided in the center of the fixed scroll is covered by the tip portion of the orbiting scroll at the final compression stage. The close contact of both inner walls prevents the compressed gas from escaping, thus creating an over-compressed state between both inner walls. This over-compression causes an excessive compressive stress which may damage the central tip portions of the scrolls.